The invention relates to a process for the recovery of the well-known preservative ortho-phenylphenol from a mixture containing such compounds as ortho-cyclohexylphenol, ortho-cyclohexylcyclohexanone, biphenyl and diphenylene oxide in addition to the ortho-phenylphenol.
Ortho-phenylphenol can be prepared by the dehydrogenation of 2-cyclohexenyl cyclohexanone, as disclosed in British patent specification No. 1,327,581; when ortho-phenylphenol is produced by said dehydrogenation method it is admixed with ortho-cyclohexylphenol, cyclohexylcyclohexanone, biphenyl and diphenylene oxide.
For use in commercial processes, the ortho-phenylphenol to be separated from such a mixture must have an ortho-cyclohexylphenol content not exceeding 5% by weight in order to be used as a carrier for dyestuffs in the textile industry and for any other application. The British Patent Specification mentioned above, discloses recovering ortho-phenylphenol from the crude reaction mixture obtained in the dehydrogenation by treating the reaction mixture with excess hydroxide solution (said excess based on the total amount of phenols present); filtering off the diphenylene oxide which then precipitates subjecting the filtrate to steam distillation; acidifying the remaining residue and extracting with ether, and then distilling the resulting product. The resulting distillate, which still contains the original amount of ortho-cyclohexylphenol in addition to the ortho-phenylphenol, can then be dehydrogenated catalytically to convert ortho-cyclohexylphenol into ortho-phenylphenol but with concomitant formation of other additional impurities.
It has now been found that this expensive processing method can be simplified considerably and a product can be obtained which contains no impurities apart from a small amount of ortho-cyclohexylphenol.